The most widely used constructional form of the underfloor forging press is the above ground type of construction.
In the above ground type of forging press, the drive is located between the upper cylinder cross head and the moving cross head which has an upper tool arranged below it. As known, this type of press has a relatively great structural height and, in consequence of the upper drive location, has a relatively high centre of gravity, which, taken together, also imply a relatively high workshop structure. On the other hand, the moving mass consists in this case only of the moving cross head with the upper tool and the plunger preferably connected therewith.
To lower the centre of gravity of the press and to reduce the structural height of the workshop, the underfloor-type construction of forging press was introduced, in which the drive is located below floor level between the fixed cross head, which also carries the lower die, and the bottom cross head--preferably constructed as the cylinder cross head. The bottom cross head, together with connecting members--usually columns--and the top cross head form a frame which carries the upper die. With each forging stroke, this frame is moved as a whole, whilst the fixed cross head remains stationary. The advantage of this construction is a low centre of gravity and the low structural height of the press above ground, which in turn implies lower and thus cheaper workshop structures. However, owing to the overall frame motion, the moving mass is greater than in the aboveground-type construction.
Thus, depending on the type of construction, the two types of press offer different advantages, but also different serious drawbacks.
For these reasons, in an open-die forging press of the underfloor type (German Patent Specification No. 1 259 180) an improvement was attempted to enable work to be carried out with high stroke frequency and low accelerations, at least during precision and high speed forging. This was achieved by means of a precision-forging or high-speed forging device accomodated in the head of the press frame. With this device, the press-frame itself need not be moved during precision and high-speed forging, so that the moving masses are substantially smaller. However, for hammer and percussion forging, with the corresponding greater stroke heights and pressing forces, the whole frame has still to be moved, whilst the drive itself is located below floor level. On the other hand, the risk of eccentric forging is particularly great precisely in hammer and percussion forging, owing to which the frame guides in the fixed cross head are subjected to particularly high stresses; furthermore, the foundation suffers owing to the high mass accelerations and decelerations producing corresponding shocks, quite apart from the intensive noise and vibrations produced even in the surroundings of the foundation.